Load connecting relay



. oq. 31, 1939. B. kNos 2,177,832

I LOAD counnc'rme RELAY Filed lay 8, 193'! INVENTOR GUNNAR SURGE K N 05 BY KZWW ATTORNEY Patented Oct. 31, 1939 UNITED STATES PATENT OFFICE LOAD CONNECTING RELAY Application May 8,1937, Serial No. 141,507 In Germany May 11, 1936 Claims.

The invention relates to a device for connecting a load to a source of current via a series resistance which is automatically switched out of circuit sometime after the establishment of 5 the connection.

' The invention may be utilized in particular with mechanically operating converting devices in which a vibrating member alternately breaks and closes again one or more circuits. .As such .0 devices known in themselves possess a certain mechanical inertia they take up, when directly connected to a mains, an excessive starting current. It is therefore necessary to connect them via a series resistance which may however be .5 switched out of a circuit again after some time, for example, a few seconds, when the device has attained its normal movement.

The use of series resistances which may be switched out of circuit automatically with some delay is known. Thus, it has been proposed inter alia to start motors via resistances having a negative temperature coeflicient. In such devices, after switching-on, the resistance is heated with the result that its resistance value gradually decreases and finally drops down to a very small value. A drawback of such resistance is that it takes a comparatively long period of time for them to cool down. Furthermore, there are known mechanically operating devices by means of which a series resistance may be gradually switched in circuit. Such devices are generally, however, rather complicated.

The problem on which the present invention is based consists in automatically switching out of circuit a single series resistance with some delay. According to the invention, this problem is solved in a simple manner by making use of a relay of which a part which functions purely thermally is influenced by the temperature of a resistance which is switched in circuit together with the load. After responding this part causes a second, for example electromagnetically actuated part to respond, owing to which the series resistance as well as the resistance which acts upon the thermal part are short-circuited, the switching members of both parts cooperating in such manner that after having cooled down the resistance remains out of circuit. The thermal part of the relay should preferably be influenced by the temperature of the series resistance itself, the contact springs of both parts cooperating in such manner that the electro-magnetic part remains in the working position even when the thermal part has returned into its position of 65 rest. The return of this part to the position of rest also takes place with some delay. In order to prevent that after a short interruption of the current of the mains during the cooling down the device is connected to the mains without series resistance, there may be provided a sec- 5 0nd series resistance which is put in circuit by the thermal part some time after the connection has been established. This putting in circuit takes place, however, prior to the response of the electro-magnetic part. Said resistance is 10 switched out of circuit again when the thermal part returns into the position of rest.

The invention will be more clearly understood by referring to the accompanying drawing which represents, by way of example, a few embodil5 ments thereof.

Fig. 1 illustrates a simplified embodiment of the invention using three contact tongues; Fig. 2 illustrates in schematic form a type of relay according to the invention incorporating four 20 tongues; and, Fig. 3 illustrates a relay constructed in accordance with the present invention and showing in more detail the coil and core arrangement.

The load 0 in Figure 1 is to be connected to 25 the mains 3 through the intermediary of a series resistance 4 which is automatically switched out of circuit after some time. To that end a switch "2 is closed whereupon the current starts flowing and the resistance 4 is gradually heated. 30 -The resistance 4 forms part of a relay which comprises three contact tongues 6, 1 and 8 and which function partly thermally and partly electromagnetically. The resistance is arranged near the tongue 6 and delivers its heat to the 35 latter. This tongue is formed, for example, as

a bimetallic strip so that it gradually bends down with the result that finally the. contact between said tongue and the tongue 1 is broken. Owin to this the short-circuit of a coil 5 connected 40 between 6 and I is removed so that this coil, which preferably should have a low ohmic resistance, is traversed by the working current. The coil 5 also forms part of the relay, namely in such manner that when it isenergized the 45 movable member 9 is raised with the result that the tongue l comes into contact with the stationary tongue 8 and the resistance 4 is shortcircuited. Then this resistance cools down again and when the circuit is interrupted the relay is 5 again ready for use. v

A further embodiment is shown in Figure 2 wherein the relay is provided with a fourth tongue it which in the position of rest is in contact with the tongue 6 so that a resistance H which has substantially the same value as the resistance 4 is short-circuited. The resistance H is either arranged so as to be separated from the relay or may be formed as a second energizing coil. The relay is constructed in such manner that when the strip 6 is heated first the contact between 6 and I 0 opened and only then the contact located between 6 and I is opened. Now the coil 5 is energized which results in the resistance 4 being short-circuited. The resistance H is still connected in series with the load I and it is not short-circuited before the-resistance 4 has cooleddown. When the resistance 4 is still hot the'resistance ll remains connected in circuit so that during this period an interrupmeans of a spring l5 in the position of rest shown in the figure. The magnetic circuit is closed via a member i8 which serves at the same time for the attachment of the contact springs 6, 1 and 8 and of the stationary part l0. These springs are separated from one another and from the other metallic parts by means of insulating pieces I6 and they are kept together by means of a strap -l'i. Around the bimetallic spring is provided a heating winding 4 which is-connected between the springs I and 8. The coil 5 is connected between the spring I and the rigid part I!) and the coil ll between the latter part and the spring 4. When the relay is energized the member I3 is attracted by the core whereupon the spring I is raised and comes into contact with the spring 8.

I claim:

1. A control device for connecting a load toa source of supply through a series resistance which is automatically switched out of the circuit after .tact springs of which the middle one, which in the position of rest is in contact with the second spring, is electromagneticaliy actuated and then comes into contact with the third and out ofcontact with the second spring, whereas the second spring responds in dependence on the temperature of a resistance, the contact with the middle spring being thus broken.

2'. A relay as claimed in claim 1, wherein the energizing coil is connected between the first and the second'contact springs and the heating resistance between the first and the third contact springs.

3. In a control'device as claimed in claim 1 further characterized by that a fourth contact spring arranged so that in the positior of rest it is in contact with the second contac spring, said contact being, broken, when the heating resistance is heated, after a period of time which is shorter than the period required for the response of the electromagnetic part and being established again when the thermal part has returned into the position of rest.

4. A control device comprising a flrstrcsistor element to be connected in a circuit, an electromagnetically operated mechanism having a coil to be connected in said circuit and a second resistor element to be connected in said circuit, a first by-pass circuit for said first resistor element, a fixed contact element and a movable contact element to connect the said by-pass circuit across said first resistor, a second by-pass circuit for the coil of said electromagnetlcally operated device, a pair of movable contact elements to connect the second by-pass circuit across saidcoil, a third by-pass circuit for said second resistor element, a fixed contact element and a movable contact element to connect the third by-pass circuit across the second resistor element, thermally operated mechanism having a. free end towhich is connected said first named movable contact and to which the second named and third named movable contacts are secured said latter two contacts being moved by said mechanism to preliminarily open said first named pair of movable contact elements and said last named fixed contact and movable contact to thereby connect in the circuit the second resistor element and the coil of the electromagnetically operated device thereby causing the last named device to become energized and means controlled thereby to cause the engagement of the first named movable contact and the first named fixed contact whereby the first named resistor is shortcircuited.

5. The arrangement described in the next preceding claim characterized by that current through the first named resistor causes the heat- -ing of said thermally operated mechanism and by 

